This invention relates to compositions of matter and methods of using them to reduce charring of reagents in the “ene” reaction. In the ene reaction a molecule is formed by the reaction of an alkene reagent with an allylic hydrogen bearing reagent. The ene reaction is often facilitated by the use of extreme reaction conditions such as high temperatures and/or strong acids. One example of an ene reaction is the thermal reaction of reagents such as maleic anhydride and an olefin to form alkenyl succinic anhydride product. Details of how to perform an ene reaction are provided in U.S. Pat. Nos. 3,819,660, 3,219,666, 3,172,892, and 3,272,746.
Because of the extreme reaction conditions, ene reactions are often accompanied by an unwanted “charring”. Charring is the degradation of some of the reagents into an insoluble, black, polymeric, solid, which resembles tar or charred material and is referred to as “char”. This degradation is sometimes accompanied by the evolution of gaseous byproducts. The formation of char is problematic because it reduces the useful yield of the ene reaction, it causes discoloration of the products, and it requires the addition of a filtration step after the ene reaction to remove the char.
One previous attempt to prevent charring described in U.S. Pat. Nos. 4,736,044 and 4,086,251 involved adding boron or chlorine to the ene reaction. Another attempt described in U.S. Pat. No. 3,412,111 involved the addition of phenols to the ene reaction. A third attempt described in U.S. Pat. No. 3,476,774 involved the addition of anilines to the ene reaction. A fourth attempt described in U.S. Pat. No. 4,235,786 involved adding acid to the ene reaction. A fifth attempt described in European Patent EP 0 319 809 A2 involved adding a combination of butylated hydroxytoluene and oxalic acid to the ene reaction. The performance of these attempts however was unsatisfying because the additives reduced product yield by failing to inhibit charring completely and by partially degrading some of the reagents into gasses, leaving less raw material to produce the desired products.
The art described in this section is not intended to constitute an admission that any patent, publication or other information referred to herein is “prior art” with respect to this invention, unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 C.F.R. §1.56(a) exists. All patents or patent applications mentioned anywhere in this application are hereby incorporated by reference in their entirety.